Conventionally, in an automatic transmission of the type in which a transmission mechanism for varying speeds stepwise or continuously variably is driven by hydraulic pressure. The hydraulic pressure supplied to the transmission mechanism is adjusted by a pressure adjusting unit controlled by a control circuit unit.
U.S. Pat. No. 5,823,070 shows an automatic transmission in which a connector case is arranged in such a way as to pass through a housing for housing a pressure adjusting unit and a control circuit unit connected to the electric components of the pressure adjusting unit is accommodated in the connector case. In the automatic transmission of this type, it is possible to realize, for example, a speed change responsive to the driving state of a vehicle by electrically connecting the control circuit unit housed in the connector case to another control circuit unit outside the housing and the electric components such as a sensor.
However, in a conventional automatic transmission in which a control circuit unit is housed in a connector case, a structure that releases heat generated by the control circuit unit itself to the outside is not employed for a connector and hence the malfunction of the control circuit unit is apt to occur. The malfunction of the control circuit unit finally causes the transmission error of the automatic transmission and hence it is extremely important to accelerate heat radiation from the control circuit unit. A method of expanding the area of the circuit board of the control circuit unit is thought as a method of accelerating heat radiation from the control circuit unit, but in the case of this method, the size of a connector is increased to increase costs, which is not desirable.